There are many applications for surveillance systems or devices for detecting or monitoring man-associated intrusions (such as personnel or vehicular traffic) within a control area, e.g. commercial establishments or private residences and security restricted or military areas. In many of these situations, a system which gives an indication of the number of intrusions in a real time readout operating mode (i.e. a continuous live monitoring operation) may be adequate. There are some applications, however, where the number of surveillance devices may be large or where the control area is remote or physically inaccessible to that it is not practical to provide a continuous real time monitoring of the devices. In these situations it would be desirable for the surveillance system to be capable of a command-readout mode of operation (i.e. the storage of information representing intrusions within the area of the device over any desired period of time and the production or broadcasting of the information upon interrogation of the device). In the latter type of operation, it may also be desirable that the device be subject to a coded command signal to prohibit unauthorized access to the information.